Metal-coated fibrillated products

ABSTRACT

LUSTROUS, METAL-COATED, FIBRILLATED PRODUCTS ARE PRODUCED BY EXTRUDING A THERMOPLASTIC POLYMER AND A FOAMING AGENT, ATTENUATING THE FOAMED EXTRUDATE WHILE IN THE MOLTEN STATE TO FIBRILLATE IT, ACTIVATING THE SURFACE OF THE FIBRILATED MATERIAL, AND DEPOSITING A THIN METALLIC COATING ON THE FIBRILLATED MATERIAL.   D R A W I N G

Aug. 10, 1971 R. G. STOLL ETAL 3,598,637

METAL-COATED FIBRILLATED PRODUCTS Filed Jan. 29, 1969 INVENTORS REINER G. STOLL JOHN A. Mc TAGGART HERBERT W. K EU CHEL ATTORNEYS United States Patent 3,598,637 METAL-COATED FIBRILLATED PRODUCTS Reiner G. Stoll, New York, N.Y., John A. McTaggart, Newark, N.J., and Herbert W. Keuchel, Charlotte, N.C., assignors to Celanese Corporation, New York,

' Filed Jan. 29, 1969, Ser. No. 794,905

Int. Cl. D04h 1/04; D02g 3/06 US. Cl. 117-107 Claims ABSTRACT OF THE DISCLOSURE This invention relates to metal-coated fibrillated products and to a process for their manufacture. More particularly, the invention relates to articles of manufacture comprising a yam-like, fibrillated thermoplastic base having a lustrous metallic surface coating that retains a desirable appearance despite wear, and to processes of making such articles.

The advent of the space age in which astronauts wearing metallicized space suits are visually featured in the news media has created an increased demand for textile materials possessing a metallic appearance, especially in high fashion dressware. There has also been a continuing requirement for metal-coated fabrics for use in heat-retentive drapery material, and for use in upholstery materials.

Spun yarns formed from all-metal, and metallicized polymeric filaments have in the past been utilized to satisfy these demands. However, yarns formed from the allmetal filaments and the metallicized polymeric filaments have been difficult and expensive to produce because of problems in the spinning operation. For example, it has been difficult to avoid loss of a uniformly metallic appearance due to abrasion of metallicized polymeric filaments during spinning.

Surface coating of previously spun yarns has not provided a product having a desirable rich, multi-tone lustrous appearance. Also, wear tends to quickly destroy the initial uniformly metallic appearance of such a surfacecoated yarn.

Accordingly, it is an object of the invention to provide novel and improved metal-coated fibrillated thermoplastic products that have good retention of their lustrous, uniformly metallic appearance.

Another object of the invention is to provide a process for preparing the novel, metal-coated products of this invention.

A further object is to provide a lustrous, yarn-like, metal-coated product that can be inexpensively manufactured, and yet retains its lustrous appearance after wear.

The invention includes a process for producing lustrous strands of a metal-coated thermoplastic product which comprises extruding a molten blend containing a thermoplastic polymer and a foaming agent to form a molten ribbon; attenuating the molten ribbon to fibrillate it before it solidifies; cooling the fibrillated ribbon to permit it to solidify; activating the surfaces of the fibrillated ribbon; and depositing a thin metallic coating on the polarized surfaces of the fibrillated ribbon.

The invention also includes a lustrous product exhibiting a desirable metallic appearance that does not rapidly disappear with wear, comprising a plurality of intercon- "ice nected thermoplastic fibrils having a thin layer of metal adherently deposited on their surfaces, with each of the fibrils having a generally irregular cross-section and separated from other fibrils along a substantial portion of its length by void spaces.

It has been discovered in accordance with the present invention that application of a metallic coating to strands of fibrillated thermoplastic material produced by hotmelt attenuation of molten ribbons of foamed polymer produces a coated article that possesses desirable and unexpected properties. Because of the novel void structure produced by the hot-melt fibrillation procedure, the metal coating material can permeate the strands to cover individual thermoplastic fibrils in a unique pattern which is not limited to the surfaces of the loosely branched strands.

Thus, the present process achieves a lustrous multi-tone reflectance effect which is distinctly superior in appearance to other metal-coated filamentary material, as, for example, those produced by the surface coating of a yarn formed of filaments of the same thermoplastic material. Further, the lustrous, uniformly metallic appearance of the articles of this invention has excellent stability and does not disappear with wear. Even when there is surface wear, such wear does not become apparent to the naked eye because of metal present throughout the void structure. This stability of appearance is probably achieved because the metallic coating remains intact on inwardly positioned fibrils even after abrasion removes some of the coating from portions of the outer surface of the exterior fibrils. Light reflected from the inwardly positioned fibrils is believed to mask the eifect of moderate wear on the exterior surfaces of the strands.

The invention consists in the novel processes, products, and improvements shown and described. The accompanying drawing, which is incorporated in and constitutes a part of this specification, serves to explain the principles of this invention.

The drawing is a schematic perspective view of equipment suitable for carrying out the process of this invention.

It is to be understood that both the foregoing general description and the following detailed description are ex emplary and explanatory but are not restrictive of the invention. Reference will now be made in detail to the present preferred embodiments of the invention.

The initial steps in the production of novel metal-coated articles according to the process of this invention comprise mixing a foaming agent and a thermoplastic polymer to form a polymer blend, heating the polymer blend, and extruding it as a molten ribbon. This extruded ribbon is fibrillated while in a molten state. Subsequently, a metallic surface coating is applied to produce a lustrous, fibrillated product.

Numerous thermoplastic polymers can be used in the production of metal-coated fibrillated products in ac cordance with the present process. In general, the process is applicable to any thermoplastic resin which can be fabricated by melt extrusion. Suitable resins include one or more polymers and/or copolymers of unsaturated compounds such as ethylene, propylene, butene, methyl-3-butene, styrene, vinyl chloride, vinylidene chloride, methyl methacrylate and methyl acrylate polyesters such as polyethylene terephthalate, polyamides such as polyhexamethylene adipamide and polycaprolactam, polyacetals, such as polyoxymethylene, polyurethanes, cellulose esters of acetic acid, propionic acid, butyric acid and the like, polycarbonate resins, and the like. Polymers which have been found to be particularly suitable for use in preparing these metal-coated, fibrillated products include polyethylene, polypropylene, polystyrene, polymethyl-3-butene, and

polyoxymethylene copolymers such as a trioxane-ethylene oxide copolymer and other polymers containing the recurring unit:

wherein each of R and R is selected from the group consisting of hydrogen, lower alkyl and halogen substituted lower alkyl radicals, and wherein n is an integer from zero to three and is zero in from 85% to 99.9% of the recurring units.

In accordance with the process of this invention a foaming agent is incorporated in the thermoplastic polymer to form a blend which is extruded and fibrillated. This foaming agent can be selected from any of the numerous solids or liquids which vaporize or decompose into gaseous products at the extrusion temperatures employed.

Solid foaming agents which can be used in the process of the present invention include azoisobutyric dinitrile, diazoamino benzene, 1,3-bis-(p-xenyl)-triazine azodicarboamide and similar azo compounds which decompose at temperatures below the extrusion temperature of the composition. Other commonly used solid foaming agents include ammonium oxalate, oxalic acid, sodium bicarbonate and oleic acid, ammonium bicarbonate, and mixtures of ammonium carbonate and sodium nitrite.

Volatile liquids which are suitable foaming agents include water, acetone, methyl ethyl ketone, ethyl acetate, methyl chloride, ethyl chloride, chloroform, methylene chloride, methylene bromide and, in general, fluorinecontaining, normally-liquid, volatile hydrocarbons. Normally gaseous foaming agents such as nitrogen, carbon dioxide, ammonia, methane, ethane, propane, ethylene, propylene, and gaseous halogenated hydrocarbons can also be used.

Another class of foaming agents consists of fluorinated hydrocarbon compounds containing from 1 to 4 carbon atoms. In addition to hydrogen and fluorine, these foaming agents may also contain chlorine or bromine. Examples of such foaming agents are dichlorodifluoromethane, dichlorofiuoromethane, chlorofluoromethane, difluoromethane, chloropentafluoroethane,

1,2-dichlorotetrafiuoroethane,

1 ,1-dichlorotetrafluoroethane,

1, l,2-trichlorotrifluoroethane, 1,1,l-trichlorotrifluoroethane, 2-chloro-1,1,1-trifluoroethane, 2-chloro-1,1,1,2-tetrafluoroethane, l-chloro-l,1,2,2-tetrafluoroethane, 1,2-dichloro-1,1,2-difiuoroethane, 1-chloro-1,1,Z-trifluoroethane, l-chloro-1,1-difiuoroethane, perfiuoropropane, 2-fluoropropane,

1 1 l ,2,2pentafluoropro pane, 1,1,l,3,3-pentafluoropropane,

1, l ,1,2,3,3-hexafluoropropane, l,l,l-trifiuoro-3-chloropropane,

trifluoromethylethylene, perfiuoropropene, and per-fluorocyclobutene.

The quantity of foaming agent employed will vary with the density of foam desired (a lower density requiring a greater amount of foaming agent), the nature of the thermoplastic resin to be foamed, and the particular foaming agents used. In general, the concentration of the foaming agent can vary from about to about 1000 cubic centimeters (at standard temperature and pressure) per 100 grams of the thermoplastic resin.

In addition to a foaming agent, the polymer melt can also contain other additives such as deodorizers and reinforcing agents.

In accordance with the invention, the polymer blend containing the foaming agent and thermoplastic polymer is formed into a molten polymer stream which is extruded as a foamed, molten ribbon. As embodied and illustrated in the drawing, the heating and extruding steps are performed in extruder 10 which extrudes a molten blend of polymer and foaming agent through a multiple slot die 12 to form a plurality of extrudate ribbons 14. The temperature of the extrudate ribbons is maintained above the melting or softening temperature of the polymeric component by means of a quench fork member 16 which subjects ribbons 14 to a flow of fluid, preferably air. This fluid stream maintains the temperature of the ribbon in the desired range.

The extrudate can be extruded as a single wide ribbon which is divided into a plurality of ribbons after fibrillation and solidification, but is preferably extruded as a plurality of narrow ribbons. The width to thickness ratio of the extruded thermoplastic ribbons can vary, but preferably ranges from about 200:1 to about 20,000:1. The width of the extruded ribbons is not changed appreciably during the subsequent processing in accordance with this invention. The thickness of the film is generally reduced during this processing.

In accordance with the invention, the molten ribbons are subjected to a hot-melt attenuating operating immediately upon leaving multiple slot die 12. Tensile forces applied to the ribbons by a takeup device attenuate the hot-melt extrudate ribbons and contribute to substantially complete fibrillation before the ribbons solidify.

As here embodied and as illustrated in the drawing, the extrudate ribbons 14 are attenuated by a takeup roller 18. The takeup speed of the hot-melt product determines the denier of the product fibrils, and the takeup speed of roller 18 thus can be varied widely depending upon the chemical nature of the thermoplastic material being extruded, and the fibril denier desired.

The exact mechanism of the production of fibrils in the melt-phase fibrillation procedure of this invention is not known. The following physical phenomena, however, have been observed. Prior to extrusion of the polymer, the foamed thermoplastic material is forced under increasing pressure into a converging film die. Under compression, the gas cells become smaller, thus storing part of the energy supplied by the extruder. On leaving the film die, the pressure on the foamed material diminishes and part of the stored energy is released in the form of cell expansion. During expansion, the cells assume an elliptical shape oriented along the stream axis of the polymer film. As the melt leaves the extrusion die, drawdown due to tension attenuates the cellular molten ribbon and causes fibrillation. The fibrillated ribbon is subsequently cooled to cause it to solidify.

A large volume of cells must be generated to yield a thermoplastic extrudate having a desirably high bulk to weight ratio. In the ideal case of equal sized bubbles, a close packing in pentagonal dodecahedrons is obtained. Packed in this arrangement, the intersection of three bubbles form three angles of degrees. In the dynamic melt-phase fibrillation process, the cell structure is never in equilibrium since shear forces and pressure and velocity gradients affect cell size and shape.

The degree of orientation of the polymer at the time of fibrillation is another factor in the successful practice of the invention. The term orientation as employed herein may be defined in terms of birefringence or X-ray diffraction. The index birefringence is calculated by the following formula:

Index of birefringence E n n wherein is the value of retardation as measured by the polarizing microscope with a Berek compensator, d is the diameter of a single extrudate, 11 is the refraction index parallel to the extrudate axis, and n is the refraction index vertical to the extrudate axis. Where the diameter of the extrudate is difiicult to measure, or is non-uniform, the index of birefringence may be obtained by measuring the refraction index parallel to the longitudinal axis of the extrudate, and perpendicular to the longitudinal axis of the extrudate, while the extrudate is disposed in an immersion fluid.

Where fibrillated products are being produced from polypropylene, it has been found that satisfactory fibrillation can be obtained by a melt-phase fibrillation process when the thermoplastic material has an index of hirefringence of less than about 0.020 and preferably from to 0.015 during the hot-melt attenuation procedure.

The degree of orientation which is required in polymeric materials other than polypropylene is best described in terms of X-ray diffraction and more specifically in terms of orientation angle. Orientation angle is a parameter which represents the alignment of molecular axes of the material forming the extrudate with respect to the longitudinal axis of the extrudate.

The orientation angles are measured according to the technique of H. G. Ingersol, Journal of Applied Physics, 17, 924 (1946) on the instrument described by I. E. Owens and W. O. Statton, Acta Crystallographic, 10, 560 (1959). In general, during the melt-phase fibrillation procedure, the thermoplastic material can have an orientation up to 180".

After fibrillation has been carried out by hot-melt attenuation of the cellular extrudate, it is desirable to orient the thermoplastic material to impart additional strength to the ribbons and to achieve smoother surfaces on the fibrils. Orientation can be accomplished by passing the ribbons through a conventional draw frame, generally 20, which comprises two pairs of draw rolls 22 with a heated shoe member 24 positioned between them. It has been found that overall draw ratios of from about 2:1 to about 8:1 are desirable for most of the thermoplastic materials used. For polypropylene, the preferred overall draw ratios are from 2:1 to :1 at a temperature of from about 110 to 145 C.

In accordance with the invention a differential shearing force, which applies a varying amount of stress across the cross-section of the fibrils, can be applied across substantially all the fibrils of the extruded and attenuated ribbon to impart a helical crimp to the fibrils and the entire ribbon, and thus texture the ribbon. If a helically crimped, textured product is not desired, this step can be omitted.

The differential shearing force is preferably applied by passing the fibrillated ribbon over a sharp edge under tension. When using certain thermoplastic materials such as polypropylene, it is desirable to transfer heat to the portion of the surface of the fibrillated ribbon that passes over the sharp, shearing edge. This heat treatment allows production of uniformly crimped material at rapid rates, and also increases the permanence of the crimp in many thermoplastic materials.

As embodied and illustrated in the drawing, the uniaxially oriented ribbon emerging from the draw frame is passed under tension over knife edge 28 to helically crimp the fibrillated ribbon. In this embodiment, the lower portion of the knife edge is intimately connected to a resistance heater 30 which is manually controlled to heat the shearing surface of the knife edge to a desired temperature.

Generally, it is desirable to maintain the temperature of knife edge 28 at about 100 to 5 C. below the melting point of the thermoplastic polymer being processed. At these temperatures, heat is rapidly transferred to the ribbons when they contact knife edge 28, allowing rapid and uniform crimping. Higher knife edge temperatures are also practical, but at such temperatures the speed of 6 the ribbons must be closely controlled to avoid overheating and melting.

Generally the ribbon should undergo a significant angular change of direction as it passes over the shearing edge. This angular change of direction can be defined in terms of angles formed by the ribbons with a reference plane that extends from the shearing edge perpendicularly to the length of the ribbons. If the approach angle, the angle of the ribbon approaching the reference plane is denoted as a and the departure angle, the angle of the ribbon departing from the plane, is denoted as ,8, then angular change of direction=180(u+B). For polypropylene, it has been found that the angular change of direction is preferably at least about 50 to produce the desired crimp parameters such as coil diameter, coil spacing, and product elongation before flattening. For polypropylene and the other polymeric ribbons described above, angular direction changes, between about 50 and 170 and preferably from to over the shearing edge provide satisfactory crimp parameters.

The passage of the width of the fibrillated ribbon over the knife edge tends to advantageously eliminate any nubs of thermoplastic material which might remain after the hot-melt attenuation step. These nubs are themselves fibrillated by the knife edge. It has been found, however, that crimping by edge snubbing can be accomplished without any substantial increase in the number of split-off fibrils in the final product. The use of such a crimping step in the process of this invention, therefore, permits formation of a desirably textured product almost totally devoid of split-off fibrils. Of course, if some fibril splitting is desired, it is also possible to severely stress the fibrils during or after edge crimping to cause such splitting.

In accordance with the process of this invention, the surfaces of the fibrillated thermoplastic strands are activated prior to depositing the metallic coating on the strands so that the surfaces will accept metal ions or molecules. This activating pretreatment can be accomplished by surface treatment with concentrated acids such as sulfuric, chlorosulfonic, or chromic acid, or by subjecting the fibrillated material to a corona discharge. The activating pretreatment of acid-resistant, thermoplastic materials, such as polypropylene, is preferably accomplished by acid treatment.

As schematically shown in the drawing, helically coiled fibrillated thermoplastic strands are treated with an acid and washed at station 34. This acid pretreatment is believed to clean and roughen the surface of the strands to insure adhesion of the subsequently-applied metal coating to the surface of the fibrils.

A metal coating is then applied to activated, pretreated strands of fibrillated thermoplastic material. The metal coating step can be carried out by a variety of procedures including vacuum metallizing and electroplating. Generally, vacuum metallizing is the most convenient and economical procedure and is preferred.

As schematically illustrated in the drawing, pretreated fibrillated strands are moved to a coating zone 36 where they are interposed between a heated source of evaporating metal and the exhaust duct of a vacuum chamber. The strands are rotated to achieve uniform metal deposition on all of the fibril surfaces, both the exterior surfaces of the fibril mass and the surfaces of the inwardly positioned fibrils of the mass. This coating produces a lustrous, uniformly metallic appearance of the articles of this invention which is characterized by an outstanding multi-tone reflectance effect and a desirable stability of appearance after wear.

A variety of metals including aluminum, zinc, chromium, copper, and various alloys of these metals can be adherently deposited on the fibrillated, thermoplastic strands. Aluminum is a particularly advantageous coating material in accordance with the present process, because 7 it is not exorbitantly expensive, and produces coatings which exhibit highly desirable luster and gloss.

The amount of the metal applied to the thermoplastic strands in accordance with the present process is not critical but preferably varies from about 0.1 to about 1.0 percent by weight of the thermoplastic fibril base material.

The product of the present process comprises a plurality of interconnected, generally longitudinally extending, helically-crimped, fibrils having an adherent, metal surface coating. The fibrils are separated from each other along a substantial portion of their length by void spaces. Immediately after the hot-melt fibrillation step, the cross-section of each fibril is generally irregular and characterized by the almost total absence of flat or planar surfaces and thus differs significantly from fibrillated materials produced by mechanically working an oriented film, a procedure which results in fibrils having a trapezoidal crosssection configuration. This unique fibril structure is an important feature in the overall, final appearance of the metal coated articles of this invention. If the optional knife edge crimping procedure is employed, portions of the present fibrils that come into contact with the edge are somewhat flattened and the fibril cross-section will thus contain some flat or planar surface portions.

The metal-coated, helically crimped, fibrillated ribbons of this invention can be further twisted, if desired, to produce products that resemble crimped, spun yarn produced from a plurality of precoated filaments. The initial appearance of the present products is superior to the appearance of surface-treated yarns, and they also exhibit improved resistance to abrasion and wear. The metal coated fibrillated products of this invention have excellent resilience and elasticity, when compared with conventional metal surface coated yarns and therefore are more suitable to use in a variety of knit and woven fabrics.

To illustrate the present invention more specifically, reference is now made to the specific examples which follow. These examples are merely illustrative and are not to be understood as limiting the scope and underlying principles of the invention in any way. All percentages referred to herein are by weight unless otherwise specifically indicated.

EXAMPLE 1 Polypropylene pellets (marketed by Hercules, Inc. under the trademark Profax 6401) having a melt index of 6.5 and an inherent viscosity of 2.2 in Decalin at 135 C. are dry-blended with 1% of azodicarbonamide blowing agent (Cellogen A.Z.). The blended polymer is placed in an extruded (see schematic process in FIG. 1) having a chrome-plated single fluted uniform pitch screw, the extruder being fitted with a die of the horizontal ribbontype, having die-slot dimensions of six (6 inches by 0.020 inch and having polymer stream dividers positioned between the lips of the die 1 /2 inches apart. The interior of the extruder is maintained at 200 C. while the diehead is maintained at a temperature of 240 C.

The polymer is extruded at a through-put rate of 20.0 grams per minute. The linear speed of the extrudate is increased by passage over a first roll having a roll speed of 20 meters per minte. A fibrillated product which is in a substantially unoriented condition is obtained almost immediately after extrusion. The extruded fibrillated ribbons are cooled at a controlled rate to a temperature below the melting or softening temperature by means of a quench fork having tubes disposed on either side of the extruded ribbons. The tubes have air orifices disposed therein, with the orifices each having a diameter of 0.04 inch and being spaced 0.125 inch apart. The temperature of the air quench is maintained at about 20 C. while the quench pressure is maintained by means of a 75 p.s.i.g. air supply.

The unoriented, fibrillated polypropylene ribbons which pass on to the first roll are subjected to a drawing and orienting operation, which is carried out by passing the ribbon over a shoe heated to 125 C. and then over a second roll having a winding speed of meters per minute, thereby producing a draw ratio of:

second roll speed first roll speed 2'5O The fibrillated polypropylene ribbon is then passed over the edge of a knife blade heated to 140 C. The ribbon is drawn in flush contact with the upstream side of the blade to effect rapid heat transfer from the blade to the ribbon. The ribbon leaves the blade inclined at an angle of 30 with respect to the downstream side of the blade so that the angular change of direction of the ribbon over the knife edge is The surface of lengths of the resulting helicallycrimped, fibrillated polypropylene strands is pretreated using various acidic solutions to activate the surface. One sample of the crimped fibrillated strands is immersed in concentrated H 80 for 5 minutes at 25 C.; another sample is immersed in concentrated H 50 for 10 minutes at 23 C.; and another sample is immersed in a solution comprising 200 cc. of concentrated H SO- 50 g. potassium bichromate, and 1 liter of water for 45 minutes at C. The latter sample is subsequently immersed in a second solution of 5 cc. of concentrated H 2 grams sodium bisulphite, and 1010 cc. water for 1 hour at 80 C. Each of the three pretreated samples and an untreated control sample are coated with aluminum by a vacuum metallizing apparatus.

All of the three samples and the control are uniformly coated and have a highly lustrous surface appearance. The metal coating on the three acid pretreated samples is firmly adherent to the surface of the fibrillated strands while the metal coating can be easily removed from the untreated control sample by contact with an adhesive tape.

A small amount of twist is applied to the three acid pretreated samples to produce strands of a yarn-like product that possess a desirable, lustrous metallic appearance. The appearance of the coating is retained even after the strands are subjected to surface wear and abrasion. The adherent. bond of the coating on the fibrillated product and the desirable surface appearance make the product suitable for use in a variety of woven and knitted fabrics.

EXAMPLE 2 A polyoxymethylene copolymer resin of a trioxaneethylene oxide copolymer marketed by Celanese Corporation under the trademark Celcon M-25 is blended with 0.7% of azodicarbonamide blowing agent and placed in an extruder. The body of the extruder is held at a temperature of 200 C. to melt the polymer blend and form a molten polymer stream which is extruded from a die head 1" wide and 0.020" deep and maintained at a temperature of 200 C. Hot-melt attenuation of the extruded ribbon produces a fibrillated ribbon which is subsequently uniaxially oriented by drawing over a heated shoe using two sets of rolls having a draw ratio of 7.4.

The oriented, fibrillated ribbon is edge crimped by passing the ribbon over a heated knife edge held at C. to obtain a tightly coiled ribbon. The ribbon approaches the knife edge parallel to the knife and departs from the knife edge inclined at an angle of 30 to the downstream side of the knife.

The surface of polyoxymethylene strands is active enough and no further activation is necessary. A uniform coating of copper is subsequently deposited on the surface of the fibrillated material in a vacuum chamber. The metal coating is firmly adherent to the copolymer substrate and produces a lustrous surface appearance.

The invention in its broader aspects is not limited to the specific details shown and described and departures may be made from such details without departing from the principles of the invention and without sacrificing its chief advantages.

What is claimed is:

1. A lustrous uniaxially oriented fabric product exhibiting a desirable and wear-stable metallic appearance and having a metallic surface coating, comprising a plurality of interconnected thermoplastic polymer fibrils, having a thin coating layer of metal adherently deposited on their surfaces, substantially all of said fibrils having a generally irregular cross-section and being separated from other fibrils along a substantial portion of its length by void spaces.

2. The product of claim 1 in which the thermoplastic polymer is polypropylene.

3. The product of claim 1 in which the thermoplastic fibrils comprise an oxymethylene polymer.

4. The product of claim 1 in which the metal coating is aluminum.

5-. The product of claim 1 in which the metal coating is copper.

6. A textured, lustrous, uniaxially oriented yarn-like product having a metallic surface coating comprising: a

plurality of interconnected thermoplastic polymer fibrils, having a generally helical configuration and being separated from other fibrils along a substantial portion of its length by void spaces, the cross-section of said fibrils being generally irregular With the exception of a fiat area formed during the helical crimping of the product; and a thin coating layer of metal adherently deposited on the surfaces of the helically crimped fibrils.

7. The product of claim 6 in which the thermoplastic polymer is polypropylene.

8. The product of claim 6 in which the thermoplastic fibrils comprise an oxymethylene polymer.

9. The product of claim 6 in which the metal is aluminum.

References Cited UNITED STATES PATENTS 2,268,160 12/1941 Miles 161Fib. 2,797,469 7/1957 Kahn 1 61-175X 2,920,981 1/1960 Whitehurst 117-160 2,974,055 3/ 1961 Scharf 161--220X 3,398,441 8/1968 Adachi et a1. 161-Fib. 3,403,203 9/1968 Schirmer 264-Fib.

ROBERT F. BURNETT, Primary Examiner R. O. UNKER, JR., Assistant Examiner US. Cl. X.R.

ll7l38.8E, R;161l73,175,177 

